1. Field of the Invention
The present invention relates to a device for supporting a patient for stereotactic on-target radiation therapy in the head region of the patient, comprising a supporting table with a tabletop movable at least in the horizontal plane, and a holding means arranged on the tabletop for arranging thereon a stereoaxis unit fixed onto the head of the patient, such holding means being associated with the head region of the patient projecting beyond the tabletop.
2. The Prior Art
When a stereotactic on-target radiation therapy has to be carried out on a patient in the head region of such patient, for example for treating brain tumor radiosurgically, a stereotaxis frame is in most cases first mounted on the head of a patient. As a rule, a computer tomography of the skull of the patient is subsequently carried out, with the stereotaxis unit fixed onto the skull. X-ray pictures of the skull of the patient are obtained in this way, with elements of the stereotaxis unit being recognizable on such pictures. It is possible with the help of these pictures to exactly determine the coordinates of the target, for example a brain tumor, to be treated with radiation therapeutically. The coordinates so found are used for focusing the treatment beam onto the target to be radiated.
The radiation treatment system of the prior art includes a device of the type specified above. Thus, there is a supporting table on which the patient is placed for the radiation treatment, whereby the patient still carries without change the stereotaxis unit; and a holding means on which this stereotaxis unit can be arranged.
The tabletop is movable at least in the horizontal plane, thus, for example, in the longitudinal direction (Z-direction) of the table, and in the transverse direction (orthogonal X-direction) of the table, so that the patient supported on the tabletop is movable in these directions as well. With the help of such movability and by reference to the stereotaxis unit fixed onto the patient, or its coordinates, it is possible to aim the radiation treatment system. This is accomplished by moving the target area within the head of the patient into the so-called iso-center of the radiation treatment system, i.e., into the center in which the radiation axis of the treatment beam and the various axes of rotation of the treatment system meet. Following this alignment of the target, a treatment can be carried out safely onto the target area of the head.
However, a problem exists in these prior art systems in that after the patient has been placed on the supporting table, the stereotaxis unit carried by the patient has to be arranged on the top of the table with the help of the holding means. Normally this requires minor movements of the stereotaxis unit until this unit fits into the holding means at the intended location because it is, of course, not possible to place the patient on the tabletop with corresponding accuracy. These adjusting and attaching movements required for securing the stereotaxis unit onto the holding means, however, are not followed by similar movements of the entire body of the patient. This is because the body of the patient, due to its mass and the frictional forces acting between the body and the tabletop, is immovable by the forces required for securing the stereotaxis unit. Instead, reactive forces build up on the body of the patient, for example due to deformation of soft body parts, which reactive forces correspond with the securing forces but are directed against the securing forces.
If the stereotaxis unit is very rigidly secured onto the head of the patient, which is sometimes done with spikes that drill themselves into bone parts of the skull of the patient, such developing reactive forces are relatively harmless because they are not capable of changing this rigid connection.
However, a less rigid connection between the stereotaxis unit and the head of the patient is sometimes selected. For example, this may result by using a thermoplastic material, which is molded onto the head of the patient like a mask, or by securing the stereotaxis unit by means of a bite block corresponding with a dental impression of the patient. In case of such less tight connection between the head of the patient and the stereotaxis unit, the reactive forces built up are then quite capable of displacing the stereotaxis unit relative to the head of the patient. This displacement can then later lead to inaccuracy in the aiming during the radiation treatment.